In reference to our chosen fort concept I remembered the floating mountains in the movie Avatar by James Cameron. They are incredibly large in comparison to the land mass I will be creating but its good for inspiration.

They have bushes growing out of the side of the mountains and the clouds give you a sence of how high the islands are floating.

I like the vines and roots hanging off the bottom and connecting the islands together. In the movie they use the vines as a way of climbing up the mountains.

You can see in this image there is moss growing in patches.

I could easily achieve some of these effects using textures for the moss on the rocks and textures with alpha channels for roots that i can put in the rocks.